IN20 - Hydrogen dynamics in the picosecond range

Hydrogen is thought to be the fuel of the future since it is abundant and non-polluting. One promising material for the storage of hydrogen is nanoscrolls (a special form of carbon nanotubes). However we still have to dominate the storage/release process and thus we must understand better how hydrogen molecules or atoms bind to carbon atoms.

Such a study is very difficult for four main reasons:

the binding energies are extremely weak, in the range of the micro eV (μeV) i.e. the picosecond time scale. This is beyond the capabilities of today's measuring techniques except for neutron spin echo (SE) spectrometry.

the measurements require both neutron triple axis spectrometry (TAS), such as IN20, which provides the energy analysis, and neutron spin echo (SE), which provides the high resolution. This combination of techniques is called TASSE and only two TASSE neutron spectrometers exist worldwide.

the sample is hydrogen but normal hydrogen (orthohydrogen) is a strong incoherent neutron scatterer which produces a strong background making measurements almost impossible. We must therefore replace orthohydrogen by parahydrogen which makes sample preparation more difficult.

the mount of adsorbed hydrogen in the sample is small compared to the amount of carbon so the very high neutron flux of the ILL reactor is really necessary.

Altogether this means that the ILL instrument IN20-TASSE is certainly the best and only one capable of carrying out such measurements.

The movie below shows the very first steps of the experiment 6-02-407 (3 to 18 nov. 2008). It was very successful and one of the results is that, below 10K, the parahydrogen line halfwidth remains roughly constant at 3 mev and the energy of this line is also constant.